Honeycomb filter

ABSTRACT

A honeycomb filter includes a honeycomb structure having a porous partition wall disposed to surround a plurality of cells; and a plugging portion provided at one end of the cell, wherein the honeycomb structure has an inflow side region including a range of up to at least 30% with respect to the total length of the honeycomb structure with the inflow end face as the starting point and an outflow side region including a range of up to at least 20% with respect to the total length of the honeycomb structure with the outflow end face as the starting point, in the extending direction of the cell of the honeycomb structure, an average pore diameter of the partition wall in the inflow side region is 9 to 14 μm and an average pore diameter of the partition wall in the outflow side region is 15 to 20 μm.

The present application is an application based on JP 2021-055970 filedon Mar. 29, 2021 with Japan Patent Office, the entire contents of whichare incorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a honeycomb filter. More particularly,the present invention relates to a honeycomb filter having excellenttrapping performance for trapping particulate matter contained inexhaust gas and excellent purification performance for purifying harmfulcomponents contained in exhaust gas.

Description of the Related Art

In recent years, regulations for removing particulate matter containedin exhaust gas emitted from gasoline engines have become stricterworldwide, and a honeycomb filter having a honeycomb structure has beenused as a filter for removing the particulate matter. Hereinafter, theparticulate matter may be referred to as “PM”. PM is an abbreviation for“Particulate Matter”.

For example, the honeycomb filter may include a honeycomb structurehaving a porous partition wall defining a plurality of cells, and aplugging portion for plugging either end of the cell. Such a honeycombfilter has a structure in which the porous partition wall serves as afilter for removing PM. Specifically, the exhaust gas containing PM isflowed in from an inflow end face of the honeycomb filter and isfiltered by trapping the PM with a porous partition wall. The purifiedexhaust gas is then discharged from an outflow end face of the honeycombfilter. In this way, PM in exhaust gas can be removed.

To improve purification performance of such a honeycomb filter, it hasbeen carried out to load a catalyst for purifying exhaust gas in aporous partition wall (see, for example, Patent Document 1). As thecatalyst for purifying exhaust gas, for example, a platinum groupelement-containing catalyst constituted by a catalyst for purifyingexhaust gas containing a platinum group element can be mentioned.Hereinafter, the platinum group element-containing catalyst may bereferred to as a “PGM catalyst”. “PGM” is an abbreviation for “PlatinumGroup Metal”. PGM includes ruthenium, rhodium, palladium, osmium,iridium, and platinum.

-   [Patent Document 1] JP-A-2015-066536

SUMMARY OF THE INVENTION

In recent years, a honeycomb filter loading the above-mentioned catalystfor purifying exhaust gas (hereinafter, simply referred to as“catalyst”) in a porous partition wall has problems in that the trappingperformance of the honeycomb filter is deteriorated and pressure loss ofthe honeycomb filter is increased. In addition, with the tightening ofexhaust gas regulation, additional measures for further improvingexhaust gas purification performance of the honeycomb filter arerequired. For example, loading of more catalysts in the porous partitionwall can improve exhaust gas purification performance; however, thedecrease in trapping performance of the honeycomb filter described abovebecomes more remarkable. Therefore, there is a need to develop ahoneycomb filter which can improve exhaust gas purification performancewithout increasing the loading amount of a catalyst and which isexcellent in trapping performance.

The present invention has been made in view of the problems with theprior arts described above. The present invention provides a honeycombfilter having excellent trapping performance for trapping PM containedin exhaust gas and excellent purification performance for purifyingharmful components contained in exhaust gas.

According to the present invention, a honeycomb filter described belowis provided.

[1] A honeycomb filter including: a honeycomb structure having a porouspartition wall disposed so as to surround a plurality of cells servingas a fluid through channel extending from an inflow end face to anoutflow end face; and a plugging portion provided so as to plug end atany one of the inflow end face side or the outflow end face side of thecell, wherein

the cells having the plugging portion at ends on the outflow end faceside and that are open on the inflow end face side are inflow cells,

the cells having the plugging portion at ends on the inflow end faceside and that are open on the outflow end face side are outflow cells,

the honeycomb structure has an inflow side region including a range ofup to at least 30% with respect to the total length of the honeycombstructure with the inflow end face of the honeycomb structure as thestarting point and an outflow side region including a range of up to atleast 20% with respect to the total length of the honeycomb structurewith the outflow end face of the honeycomb structure as the startingpoint, in the extending direction of the cell of the honeycombstructure,

an average pore diameter of the partition wall in the inflow side regionis 9 to 14 μm and an average pore diameter of the partition wall in theoutflow side region is 15 to 20 μm.

[2] The honeycomb filter according to [1], wherein a porosity of thepartition wall is 50 to 65% and a thickness of the partition wall is0.19 to 0.31 mm.

[3] The honeycomb filter according to [1] or [2], wherein a cell densityof the honeycomb structure is 30 to 50 cells/cm².

[4] The honeycomb filter according to any one of [1] to [3], furtherincludes a catalyst for purifying exhaust gas loaded on the partitionwall constituting the honeycomb structure, wherein the catalyst forpurifying exhaust gas is loaded at least on the surface of the partitionwall, in the inflow side region of the honeycomb structure.

[5] The honeycomb filter according to [4], wherein the catalyst forpurifying exhaust gas includes a platinum group element-containingcatalyst.

[6] The honeycomb filter according to [5], wherein the platinum groupelement-containing catalyst includes an oxide of at least one element ofaluminum, zirconium, and cerium.

[7] The honeycomb filter according to any one of [4] to [6], wherein aloading amount of the catalyst for purifying exhaust gas per unit volumeof the honeycomb structure is less than 50 g/L.

The honeycomb filter of the present invention has effects of havingexcellent trapping performance for trapping PM contained in exhaust gasand also having excellent purification performance for purifying harmfulcomponents contained in exhaust gas when using a porous partition wallloaded with a catalyst for purifying exhaust gas. In particular, thehoneycomb filter of the present invention can improve purificationperformance without increasing the loading amount of a catalyst forpurifying exhaust gas, and can also improve trapping performance.

That is, the honeycomb filter of the present invention has an inflowside region with an average pore diameter of 9 to 14 μm in a range of atleast 30% of the total length of the honeycomb structure with the inflowend face of the honeycomb structure as the starting point, in theextending direction of the cell of the honeycomb structure. The inflowside region is configured so that the average pore diameter of thepartition wall is relatively small, and when the catalyst for purifyingexhaust gas is loaded, it is difficult to penetrate the catalyst forpurifying exhaust gas into the pores formed on the partition wall.Therefore, when the catalyst for purifying exhaust gas is loaded on thehoneycomb filter, in the above-described inflow side region, thecatalyst for purifying exhaust gas is preferentially loaded on thesurface of the partition wall, and a catalyst layer in which thecatalyst for purifying exhaust gas is deposited is formed on the surfaceof the partition wall. In particular, as described above, since it isdifficult to penetrate the catalyst for purifying exhaust gas into thepores formed on the partition wall in the inflow side region, a catalystlayer having a sufficient thickness is formed on the surface of thepartition wall even if the loading amount of the catalyst is small. Forthis reason, in the inflow side region, the contact between the catalystlayer on the surfaces of the partition wall and exhaust gas isincreased, and exhaust gas purification performance can be effectivelyimproved. On the other hand, the honeycomb filter of the presentinvention has an outflow side region with an average pore diameter of 15to 20 μm in a range of at least 20% of the total length of the honeycombstructure with the outflow end face of the honeycomb structure as thestarting point, in the extending direction of the cell of the honeycombstructure. When the loading amount of the catalyst for purifying exhaustgas to the honeycomb filter is small, the loading amount of the catalystin the outflow side region is relatively reduced relative to the loadingamount of the catalyst in the inflow side region. In addition, even ifthe catalyst for purifying exhaust gas is loaded, the catalyst forpurifying exhaust gas penetrates into the pores formed on the partitionwall, and a cake layer such as a catalyst layer is hardly formed in theoutflow side region. Therefore, the porous partition wall in the outflowside region effectively functions as a filter medium for trapping PM,and excellent trapping performance can be realized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a first embodiment ofthe honeycomb filter of the present invention.

FIG. 2 is a plan view of the inflow end face side of the honeycombfilter shown in FIG. 1 .

FIG. 3 is a plan view of the outflow end face side of the honeycombfilter shown in FIG. 1 .

FIG. 4 is a sectional view schematically showing a section taken alongthe line A-A′ of FIG. 2 .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following will describe embodiments of the present invention;however, the present invention is not limited to the followingembodiments. Therefore, it should be understood that those created byadding changes, improvements or the like to the following embodiments,as appropriate, on the basis of the common knowledge of one skilled inthe art without departing from the spirit of the present invention arealso covered by the scope of the present invention.

(1) Honeycomb Filter:

A first embodiment of the honeycomb filter of the present invention isthe honeycomb filter 100 as shown in FIGS. 1 to 4 . FIG. 1 is aperspective view schematically showing the first embodiment of thehoneycomb filter of the present invention. FIG. 2 is a plan view of aninflow end face side of the honeycomb filter shown in FIG. 1 . FIG. 3 isa plan view of an outflow end face side of the honeycomb filter shown inFIG. 1 . FIG. 4 is a sectional view schematically showing the sectiontaken along the line A-A′ of FIG. 2 .

As shown in FIGS. 1 to 4 , the honeycomb filter 100 of the presentembodiment is provided with a honeycomb structure 4 and a pluggingportion 5. The honeycomb structure 4 has a porous partition wall 1disposed so as to surround a plurality of cells 2 serving as a fluidthrough channel extending from the inflow end face 11 to the outflow endface 12. The honeycomb structure 4 shown in FIGS. 1 to 4 is configuredin a round-pillar shape with the inflow end face 11 and the outflow endface 12 as both end faces, and further has a circumferential wall 3 onthe outer peripheral side surface thereof. In other words, thecircumferential wall 3 is disposed to encompass the partition wall 1disposed in a grid pattern.

The plugging portion 5 is provided so as to plug end at any one of theinflow end face 11 side or the outflow end face 12 side of the cell 2.Hereinafter, among the plurality of cells 2, the cell 2 in which theplugging portion 5 is disposed at the end on the outflow end face 12side and the inflow end face 11 side is opened is referred to as the“inflow cell 2 a”. In addition, among the plurality of cells 2, the cell2 in which the plugging portion 5 is disposed at the end on the inflowend face 11 side and the outflow end face 12 side is opened is referredto as the “outflow cell 2 b”. In the honeycomb filter 100 of the presentembodiment, it is preferable that the inflow cells 2 a and the outflowcells 2 b are alternately arranged with the partition wall 1 interposedtherebetween.

The honeycomb filter 100 is characterized in that the honeycombstructure 4 is configured as follows. The honeycomb structure 4 has aninflow side region 15 including a range of up to at least 30% withrespect to the total length L1 of the honeycomb structure 4 with theinflow end face 11 of the honeycomb structure 4 as the starting point,in the extending direction of the cell 2 of the honeycomb structure 4.In addition, the honeycomb structure 4 has an outflow side region 16including a range of up to at least 20% with respect to the total lengthL1 of the honeycomb structure 4 with the outflow end face 12 of thehoneycomb structure 4 as the starting point, in the extending directionof the cell 2 of honeycomb structure 4. That is, in the honeycombstructure 4, the length L2 of the inflow side region 15 in the extendingdirection of the cell 2 is at least 30% with respect to the total lengthL1 of the honeycomb structure 4, and the length L3 of the outflow sideregion 16 in the extending direction of the cell 2 is at least 20% withrespect to the total length L1 of the honeycomb structure 4, as shown inFIG. 4 .

Hereinafter, the ratio (%) of the length of the inflow side region 15with respect to the total length L1 of the honeycomb structure 4 withthe inflow end face 11 of the honeycomb structure 4 as the startingpoint may be referred to as a “length range (%) from the inflow end face11 of the inflow side region 15”. In addition, the ratio (%) of thelength of the outflow side region 16 with respect to the total length L1of the honeycomb structure 4 with the outflow end face 12 of thehoneycomb structure 4 as the starting point may be referred to as a“length range (%) of the outflow side region 16 from the outflow endface 12”.

In the honeycomb filter 100 of the present embodiment, an average porediameter of the partition wall 1 in the inflow side region 15 is 9 to 14μm and an average pore diameter of the partition wall 1 in the outflowside region 16 is 15 to 20 μm. That is, in the honeycomb filter 100, theaverage pore diameter of the partition wall 1 is relatively small in theinflow side region 15 of the honeycomb structure 4, while the averagepore diameter of the partition wall 1 is relatively large in the outflowside region 16 of the honeycomb structure 4. The average pore diametersof the partition wall 1 in the inflow side region 15 and the outflowside region 16 of the honeycomb structure 4 are measured by the mercurypress-in method. The average pore diameter of the partition wall 1 canbe measured by using, for example, Autopore 9500 (trade name)manufactured by Micromeritics.

The honeycomb filter 100 is excellent in trapping performance fortrapping PM contained in exhaust gas and also excellent in purificationperformance for purifying harmful components contained in exhaust gas,when using a porous partition wall 1 loaded with a catalyst forpurifying exhaust gas.

In other words, in the honeycomb filter 100, it is difficult topenetrate the catalyst for purifying exhaust gas into the pores formedon the partition wall 1 in the inflow side region 15 in which theaverage pore diameter of the partition wall 1 is 9 to 14 μm, when usingthe porous partition wall 1 loaded with the catalyst for purifyingexhaust gas. Therefore, when the catalyst for purifying exhaust gas isloaded on the honeycomb filter 100, the catalyst for purifying exhaustgas is preferentially loaded on the surface of the partition wall 1 inthe inflow side region 15, and a catalyst layer in which the catalystfor purifying exhaust gas is deposited is formed on the surface of thepartition wall 1. In particular, as described above, since it isdifficult to penetrate the catalyst for purifying exhaust gas into thepores formed on the partition wall 1 in the inflow side region 15, acatalyst layer having a sufficient thickness is formed on the surface ofthe partition wall 1 even if the loading amount of the catalyst issmall. For this reason, in the inflow side region 15, the contactbetween the catalyst layer on the surfaces of the partition wall 1 andexhaust gas is increased, and exhaust gas purification performance canbe effectively improved. On the other hand, in the outflow side region16 in which the average pore diameter of the partition wall 1 is 15 to20 μm, when the catalyst for purifying exhaust gas is loaded, theloading amount of the catalyst is relatively reduced relative to theloading amount of the catalyst in the inflow side region 15. Inaddition, even if the catalyst for purifying exhaust gas is loaded, thecatalyst for purifying exhaust gas penetrates into the pores formed onthe partition wall 1, and a cake layer such as a catalyst layer ishardly formed in the outflow side region 16. Therefore, the porouspartition wall 1 in the outflow side region 16 effectively functions asa filter medium for trapping PM, and excellent trapping performance canbe realized.

The confirmation method of the inflow side region 15 and the outflowside region 16 of the honeycomb structure 4 and the measuring method ofthe average pore diameters of the partition wall 1 in the inflow sideregion 15 and the outflow side region 16 are as follows. First, 5measuring points are determined in 1% increments with respect to thetotal length L1 of the honeycomb structure 4 with the inflow end face 11as the starting point. Then, a part of the partition wall 1 of thehoneycomb structure 4 is cut out from each of the measurement pointsdescribed above, and a sample piece for measurement for measuring theaverage pore diameter is obtained, respectively. As the sample piece formeasurement, for example, a rectangular parallelepiped having a length,a width, and a height of approximately 10 mm, approximately 10 mm, andapproximately 10 mm, respectively, is used. Then, each average porediameter (i.e., an average pore diameter in 1% increments with respectto the total length L1 of the honeycomb structure 4 with the inflow endface 11 as the starting point) is measured for each sample piece formeasurement by the mercury press-in method.

In measuring the average pore diameter described above, a range in whichthe average pore diameter of the partition wall 1 with the inflow endface 11 as the starting point is 9 to 14 μm is the “inflow side region15”. Further, a ratio of the length of the range in which the averagepore diameter of the partition wall 1 with respect to the total lengthL1 of the honeycomb structure 4 with the inflow end face 11 as thestarting point is 9 to 14 μm (i.e., inflow side region 15) is the“length range (%) from the inflow end face 11 of the inflow side region15”.

Similarly, in measuring the average pore diameter described above, arange in which the average pore diameter of the partition wall 1 withthe outflow end face 12 as the starting point is 15 to 20 μm is the“outflow side region 16”. Further, a ratio of the length of the range inwhich the average pore diameter of the partition wall 1 with respect tothe total length L1 of the honeycomb structure 4 with the outflow endface 12 as the starting point is 15 to 20 μm (i.e., outflow side region16) is the “length range (%) from the outflow end face 12 of the outflowside region 16”.

In the honeycomb filter 100 of the present embodiment, the inflow sideregion 15 is in the range of up to at least 30% with respect to thetotal length L1 of the honeycomb structure 4 with the inflow end face 11as the starting point. On the other hand, the outflow side region 16 isin the range of up to at least 20% with respect to the total length L1of the honeycomb structure 4 with the outflow end face 12 as thestarting point. Therefore, the honeycomb structure 4 may further have an“intermediate region 17” other than inflow side region 15 and outflowside region 16 in a part of the range of 30 to 80% in the total lengthL1 direction of the honeycomb structure 4 with the inflow end face 11 asthe starting point in the extending direction of the cell 2 of honeycombstructure 4. The intermediate region 17 is a region which does notsatisfy the respective numerical ranges of the average pore diameters ofthe partition wall 1 in the inflow side region 15 and the outflow sideregion 16 and is not included in any of the regions. It is needless tosay that the honeycomb structure 4 does not have the intermediate region17 as described above, and the predetermined length range with theinflow end face 11 as the starting point may be the inflow side region15, and the remaining length range may be the outflow side region 16.

In the intermediate region 17 of the honeycomb structure 4, the averagepore diameter of the partition wall 1 in the intermediate region 17 ispreferably greater than 14 μm and less than 15 μm. For example, when theaverage pore diameter of the honeycomb structure 4 is 9 to 14 μm in therange of 50% and is 14 to 15 μm in the range of 50 to 70%, with respectto the total length L1 of the honeycomb structure 4 with the inflow endface 11 as the starting point, the range of the 50% described above isthe inflow side region 15 and the range of 50 to 70% is the intermediateregion 17. Then, for example, when the average pore diameter in theremaining range of 70 to 100% with respect to the total length L1 of thehoneycomb structure 4 with the inflow end face 11 as the starting pointis 15 to 20 μm, this remaining range (range of 70 to 100%) is theoutflow side region 16.

As shown in FIG. 4 , in the honeycomb structure 4, the length L2 in theextending direction of the cell 2 in the inflow side region 15 is atleast 30% with respect to the total length L1 of the honeycomb structure4 and is at most 80% with respect to the total length L1 of thehoneycomb structure 4. The length L2 in the extending direction of thecell 2 in the inflow side region 15 is not particularly limited, but ispreferably, for example, 30 to 60%, more preferably 30 to 50%, withrespect to the total length L1 of the honeycomb structure 4.

In the honeycomb structure 4, the length L3 in the extending directionof the cell 2 in the outflow side region 16 is at least 20% with respectto the total length L1 of the honeycomb structure 4, and is at most 70%with respect to the total length L1 of the honeycomb structure 4. Thelength L3 in the extending direction of the cell 2 in the outflow sideregion 16 is not particularly limited, but is preferably, for example,20 to 40%, more preferably 20 to 30%, with respect to the total lengthL1 of the honeycomb structure 4.

In honeycomb structure 4, the intermediate region 17 is an optionalcomponent as described above, and the length L4 in the extendingdirection of the cell 2 in the intermediate region 17 is at most 50%with respect to the total length L1 of the honeycomb structure 4. Thelength L4 in the extending direction of the cell 2 in the intermediateregion 17 can be appropriately set in accordance with the length L2 inthe extending direction of the cell 2 in the inflow side region 15 andthe length L3 in the extending direction of the cell 2 in the outflowside region 16 described above.

The average pore diameter of the partition wall 1 in the inflow sideregion 15 is 9 to 14 μm, preferably 9 to 13 μm, and more preferably 9 to12 μm. The average pore diameter of the partition wall 1 in the outflowside region 16 is 15 to 20 μm, preferably 15 to 19 μm, and morepreferably 15 to 17 μm.

A porosity of the partition wall 1 of the honeycomb structure 4 ispreferably 50 to 65%, more preferably 55 to 65%, and particularlypreferably 60 to 65%. The porosity of the partition wall 1 is measuredby the mercury press-in method. The porosity of the partition wall 1 canbe measured by using, for example, Autopore 9500 (trade name)manufactured by Micromeritics. If the porosity of the partition wall 1is less than 50%, it is not preferable in that the permeabilityresistance of the partition wall increases and pressure loss increases.If the porosity of the partition wall 1 exceeds 65%, it is notpreferable in that the strength is remarkably deteriorated.

The honeycomb structure 4 preferably has a thickness of the partitionwall 1 of 0.19 to 0.31 mm, more preferably 0.22 to 0.31 mm, andparticularly preferably 0.22 to 0.28 mm. The thickness of the partitionwall 1 can be measured with a scanning electron microscope or amicroscope, for example. If the thickness of the partition wall 1 isless than 0.19 mm, adequate strength may not be obtained in some cases.On the other hand, if the thickness of partition wall 1 exceeds 0.31 mm,pressure loss may increase when the catalyst is loaded on the partitionwall 1.

A shape of the cells 2 formed in the honeycomb structure 4 is notparticularly limited. For example, the shape of the cells 2 in thesection orthogonal to the extending direction of the cells 2 may bepolygonal, circular, elliptical or the like. Examples of the polygonalshape include a triangle, a quadrangle, a pentagon, a hexagon, and anoctagon. The shape of the cells 2 is preferably triangular,quadrangular, pentagonal, hexagonal or octagonal. Further, regarding theshapes of the cells 2, all the cells 2 may have the same shape ordifferent shapes. For example, although not shown, quadrangular cellsand octagonal cells may be combined. Further, regarding the sizes of thecells 2, all the cells 2 may have the same size or different sizes. Forexample, although not shown, some of the plurality of cells may belarger, and other cells may be smaller relatively. In the presentinvention, the cell means a space surrounded by the partition wall.

The cell density of the cell 2 defined by the partition wall 1 ispreferably 30 to 50 cells/cm², more preferably 35 to 50 cells/cm². Withthis configuration, it is possible to suitably use as a filter fortrapping PM in exhaust gas emitted from engines of automobiles or thelike.

The circumferential wall 3 of the honeycomb structure 4 may beintegrally formed with the partition wall 1, or may be a circumferentialcoating layer formed by applying a circumferential coating material soas to encompass the partition wall 1. Although not shown, during themanufacturing, the partition wall and the circumferential wall areintegrally formed and then the formed circumferential wall may beremoved by a well-known method such as grinding. Then, the circumferencecoating layer may be provided on the circumferential side of thepartition wall.

A shape of the honeycomb structure 4 is not particularly limited. Theshape of the honeycomb structure 4 includes pillar-shaped in which theshapes of the inflow end face 11 and the outflow end face 12 arecircular, elliptical, polygonal, or the like.

A size of the honeycomb structure 4, for example, the length in theextending direction of the cell 2 of the honeycomb structure 4(hereinafter, also referred to as “total length L1”) and the size of thesection orthogonal to the extending direction of the cell 2 of thehoneycomb structure 4 (hereinafter, also referred to as “sectionalarea”) is not particularly limited. Each size may be selected asappropriate such that optimum purification performance is obtainedduring use of the honeycomb filter 100. The total length L1 of thehoneycomb structure 4 is preferably 90 to 160 mm, more preferably 120 to140 mm. In addition, the sectional area of the honeycomb structure 4 ispreferably 8000 to 16000 mm², more preferably 10000 to 14000 mm².

The material of the partition wall 1 preferably contains at least oneselected from the group consisting of cordierite, silicon carbide,silicon-silicon carbide composite material, mullite, alumina, aluminumtitanate, silicon nitride, and silicon carbide-cordierite compositematerial. The material constituting the partition wall 1 preferablycontains the materials listed in the above group in an amount of 30% bymass or more, more preferably 40% by mass or more, and particularlypreferably 50% by mass or more. In the honeycomb filter 100 of thepresent embodiment, the material constituting the partition wall 1 isparticularly preferably cordierite.

The honeycomb structure 4 is preferably an integrally formed productmade of the materials constituting the partition wall 1 described above.That is, it is preferable that the honeycomb structure 4 in thehoneycomb filter 100 is not produced by connecting the inflow sideregion 15 and the outflow side region 16 which are produced separately,but is an integrally formed product that is integrally formed by usingpredetermined forming materials.

The honeycomb filter 100 may further include a catalyst for purifyingexhaust gas (not shown) loaded on the partition wall 1 constituting thehoneycomb structure 4. The catalyst for purifying exhaust gas ispreferably loaded at least on the surface of the partition wall 1 ininflow side region 15 of the honeycomb structure 4. Here, “loaded atleast on the surface of the partition wall 1” means that the catalystfor purifying exhaust gas may be loaded only on the surface of thepartition wall 1, or may be loaded on the surface and inside the pore ofthe partition wall 1. “Loaded only on the surface of the partition wall1” means that the catalyst is present on the surface of the partitionwall 1 in the thickness direction of the partition wall 1, and that thecatalyst for purifying exhaust gas is not present between 0.1T and 1.0T(where T represents the thickness of the partition wall 1) in thethickness direction of the partition wall 1 from the surface of thepartition wall 1 on the inflow cell 2 a side of the partition wall 1.“Loaded on the surface and inside the pore of the partition wall 1”means that the catalyst is present on the surface of the partition wall1, and that the catalyst for purifying exhaust gas is present at leastsomewhere between 0.1T and 0.9T (where T represents the thickness of thepartition wall 1) in the thickness direction of the partition wall 1from the surface of the partition wall 1 on the inflow cell 2 a side ofthe partition wall 1. On the other hand, it is preferable that thecatalyst for purifying exhaust gas is not loaded in the outflow sideregion 16 of the honeycomb structure 4. If the catalyst for purifyingexhaust gas is loaded in the outflow side region 16, it may be loadedinside the pore formed on the partition wall 1. “Loaded inside the poreof the partition wall 1” means that the catalyst for purifying exhaustgas is present at least somewhere between 0.1T and 0.9T (where Tindicates the thickness of the partition wall 1) in the thicknessdirection of the partition wall 1 from the surface of the partition wall1 of the inflow cell 2 a side of the partition wall 1. With thisconfiguration, a catalyst layer in which the catalyst for purifyingexhaust gas is deposited on the surface of the partition wall 1 isformed in the inflow side region 15. In particular, since the catalystfor purifying exhaust gas is difficult to penetrate into the pore formedon the partition wall 1 in the inflow side region 15, the catalyst layerhaving a sufficient thickness is formed on the surface of the partitionwall 1 even if the loading amount of the catalyst is small. Therefore,in the inflow side region 15, the contact between the catalyst layer onthe surfaces of the partition wall 1 and the exhaust gas increases, andexhaust gas purification performance can be effectively improved. Inaddition, the porous partition wall 1 in the outflow side region 16effectively functions as a filter medium for trapping PM, and excellenttrapping performance can be realized.

In the honeycomb filter 100 further comprising a catalyst for purifyingexhaust gas, as described above, it is preferable to differ loading formof the catalyst in the inflow side region 15 and the outflow side region16 having different sizes of the average pore diameter. Since thehoneycomb filter 100 differs in the average pore diameter of thepartition wall 1 in two regions of the inflow side region 15 and theoutflow side region 16, for example, one type of a slurry for catalystloading (e.g., a catalyst liquid) can be used to change loading form ofthe catalyst with respect to each region. In particular, loading form ofthe catalyst for the desired region can be conveniently changed by onecatalyst loading step. Therefore, according to the honeycomb filter 100of the present embodiment, the honeycomb filter 100 further comprising acatalyst for purifying exhaust gas as described above is possible toextremely conveniently manufactured.

Note that, in inflow side region 15, as described above, a part of thecatalyst may be loaded inside the pore formed on the partition wall 1 aslong as the catalyst is loaded on at least the surface of the partitionwall 1. However, in the inflow side region 15, when the catalyst isloaded, the catalyst is difficult to penetrate inside the pore, so thatthe catalyst is preferentially loaded on the surface of the partitionwall 1, and even if the loading amount of the catalyst is small, thecatalyst layer having a sufficient thickness can be formed on thesurface of the partition wall 1. Therefore, according to the honeycombfilter 100 of the present embodiment, the amount of the catalyst forpurifying exhaust gas (in other words, the loading amount) can bereduced.

It is preferable that the catalyst for purifying exhaust gas which isloaded in the partition wall 1 constituting the honeycomb structure 4contains a platinum group element-containing catalyst. The platinumgroup element-containing catalyst is a catalyst for purifying exhaustgas containing a platinum group element. The platinum group elements areruthenium, rhodium, palladium, osmium, iridium, and platinum.Hereinafter, the platinum group element may be referred to as “PGM”.Since the catalyst for purifying exhaust gas contains a platinum groupelement-containing catalyst, the effect of excellent purificationperformance for purifying harmful components contained in exhaust gas isexhibited. In the honeycomb filter 100 of the present embodiment, it ispreferable that the catalyst for purifying exhaust gas loaded on thepartition wall 1 is substantially a platinum group element-containingcatalyst.

The platinum group element-containing catalyst preferably contains anoxide of at least one element of aluminum, zirconium, and cerium. Thecatalyst containing such an oxide preferably contains 1 to 3% by mass ofa platinum group element based on the total mass of the catalyst. Thecomposition of the platinum group element-containing catalyst can bemeasured, for example, by X-ray Fluorescence (XRF) analysis.Specifically, the composition analysis of the platinum groupelement-containing catalyst is performed by detecting the fluorescentX-ray inherent in each element, which is generated by irradiating thesample with X-rays.

The loading amount of the catalyst for purifying exhaust gas per unitvolume of the honeycomb structure 4 is not particularly limited, but ispreferably, for example, less than 50 g/L, more preferably 30 g/L ormore and less than 50 g/L, and particularly preferably 40 g/L or moreand less than 50 g/L. Note that the loading amount of the catalyst forpurifying exhaust gas is the mass (g) of the catalyst loaded per 1 L ofthe volume of the honeycomb structure 4. The loading method of thecatalyst for purifying exhaust gas includes a method in which thehoneycomb structure 4 is wash-coated with a catalyst liquid containing acatalyst component, and then heat-treated at a high temperature andbaked, for example.

(2) Manufacturing Method of Honeycomb Filter:

A manufacturing method of the honeycomb filter of the present inventionis not particularly limited, and the honeycomb filter can bemanufactured by the following method, for example.

First, a plastic kneaded material for producing a partition wall of thehoneycomb structure is prepared. The kneaded material for producing thepartition wall of the honeycomb structure can be prepared by adding, asappropriate, an additive such as a binder, pore former, and water to araw material powder for producing suitable materials of the partitionwall described above. As the raw material powder, for example, a powderof alumina, talc, kaolin, or silica can be used. Examples of the binderinclude methylcellulose and hydroxypropyl methylcellulose. Examples ofthe additives include surfactant.

Next, the kneaded material thus obtained is extruded, thereby producinga pillar-shaped honeycomb formed body having a partition wall defining aplurality of cells and a circumferential wall disposed so as to surroundthe partition wall. Next, the obtained honeycomb formed body is dried bymicrowaves and hot air, for example.

Next, a plugging portion is formed on the dried honeycomb formed body.The plugging portion can be formed according to a conventionally knownmanufacturing method of honeycomb filter. For example, first, the inflowend face of the honeycomb formed body is provided with a mask so thatthe inflow cell is covered. Thereafter, the end of the honeycomb formedbody provided with the mask is immersed in the plugging slurry, and theplugging slurry is filled into the open end of the unmasked outflowcell. Thereafter, for the outflow end face of the honeycomb formed body,the plugging slurry is filled into the open end of the inflow cell inthe same manner as described above. Thereafter, the honeycomb formedbody with the plugging portion is further dried in a hot air dryer.

The honeycomb formed body with the plugging portion is then fired tomanufacture a honeycomb filter provided with a honeycomb structure and aplugging portion disposed so as to plug either end of the cell. Thefiring temperature and the firing atmosphere for firing the honeycombformed body differ depending on the raw material from which thehoneycomb formed body is made, and a skill in art can select the firingtemperature and the firing atmosphere that are optimal for the selectedmaterials.

When manufacturing the honeycomb filter of the present invention, theaverage pore diameter of the partition wall of the obtained honeycombstructure is adjusted by the following process. That is, the averagepore diameter of the partition wall in the inflow side region of theobtained honeycomb structure is adjusted to 9 to 14 μm, and the averagepore diameter of the partition wall in the outflow side region isadjusted to 15 to 20 μm. Specifically, when manufacturing the honeycombfilter by firing the honeycomb formed body, the difference between thetemperature in the filter of the inflow end face side and thetemperature in the filter of the outflow end face side is adjusted to10° C. or higher. Thus, the average pore diameter of the partition wallconstituting the honeycomb filter can be adjusted by providing thedifference above a predetermined temperature inside the honeycomb formedbody at the inflow end face side and the outflow end face side duringfiring.

EXAMPLES

The following will describe the present invention more specifically byway of examples, but the present invention is not at all limited by theexamples.

Example 1

First, raw materials of alumina, talc, kaolin, and silica for producinga partition wall of the honeycomb structure were prepared. To theprepared raw materials of alumina, talc, kaolin, and silica, 2 parts bymass of dispersing medium and 7 parts by mass of an organic binder wereadded, respectively, and mixed and kneaded to prepare a kneadedmaterial. As the dispersing medium, water was used. As the organicbinder, methylcellulose was used. As dispersing agent, surfactant wasused.

Next, the kneaded material was extruded using a die for manufacturing ahoneycomb formed body to obtain the honeycomb formed body having a roundpillar shape as the overall shape. The cells of the honeycomb formedbody had a quadrangular shape.

Next, the honeycomb formed body was dried by a microwave dryer and driedcompletely by a hot-air drier, and then both end faces of the honeycombformed body were cut so as to have predetermined dimensions.

Next, a plugging portion was formed on the dried honeycomb formed body.Specifically, first, the inflow end face of the honeycomb formed bodywas provided with a mask so that the inflow cell was covered.Thereafter, the end of the honeycomb formed body provided with the maskwas immersed in the plugging slurry, and the plugging slurry was filledinto the open end of the unmasked outflow cell. Thereafter, for theoutflow end face of the honeycomb formed body, the plugging slurry wasfilled into the open end of the inflow cell in the same manner asdescribed above. Thereafter, the honeycomb formed body with the pluggingportion was further dried in a hot air dryer.

Next, the dried honeycomb formed body was degreased and fired to producea honeycomb filter of Example 1. In Example 1, the average pore diameterof the partition wall constituting the honeycomb filter was adjusted byadjusting the temperature distribution in the firing process.

Next, the partition wall of the honeycomb filter of Example 1 was loadedwith a platinum group element-containing catalyst by the followingmethod. First, a slurry for forming a catalyst layer containing a powderof an aluminum oxide obtained by loading palladium as a platinum groupelement, ion-exchanged water, and dispersing agent was prepared. Next,the slurry for forming a catalyst layer was poured from the inflow endface of the honeycomb filter, and the poured slurry for forming acatalyst layer was sucked from the outflow end face at an appropriatesuction amount so that the platinum group element-containing catalystlayer was applied to the partition wall. Thereafter, the platinum groupelement-containing catalyst applied to the partition wall was fired at500° C., and the platinum group element-containing catalyst was loadedon the partition wall of the honeycomb filter of Example 1. In Example1, the platinum group element-containing catalyst was loaded by theabove method so that the loading amount of the platinum groupelement-containing catalyst per unit volume of the honeycomb structurewas 40 g/L. The loading amount of the platinum group element-containingcatalyst is shown in the column of “Catalyst loading amount (g/L)” inTable 1.

The honeycomb filter of Example 1 had a round-pillar shape, where theinflow end face and the outflow end face were round. The length of thehoneycomb filter in the extending direction of the cell was 127 mm. Thediameter of end face of the honeycomb filter was 118 mm. In thehoneycomb structure constituting the honeycomb filter, the thickness ofthe partition wall was 0.216 mm and the cell density was 46.5 cells/cm².The porosity of the partition wall of the honeycomb structure was 63%.The cell density, partition wall thickness and porosity are shown inTable 1.

Further, the honeycomb filter of Example 1 had the average pore diameterof the partition wall of 13 μm in the range up to 40% with respect tothe total length of the honeycomb structure with the inflow end face ofthe honeycomb structure as the starting point. Therefore, in thehoneycomb filter of Example 1, the range of up to 40% with respect tothe total length of the honeycomb structure with the inflow end face ofthe honeycomb structure as the starting point was the inflow side regionin which the average pore diameter of the partition wall was 9 to 14 μm.Further, the honeycomb filter of Example 1 had the average pore diameterof partition wall of 20 μm in the range of up to 40% with respect to thetotal length of the honeycomb structure with the outflow end face of thehoneycomb structure as the starting point. For this reason, in thehoneycomb filter of Example 1, the range of up to 40% with respect tothe total length of honeycomb structure with the outflow end face of thehoneycomb structure as the starting point was the outflow side region inwhich the average pore diameter of the partition wall was 15 to 20. Theresults are shown in the columns “Average pore diameter (m)” and “Lengthrange from inflow end face (%)” of “Inflow side region”, and “Averagepore diameter (μm)” and “Length range from outflow end face (%)” of“Outflow side region” in Table 1.

TABLE 1 Inflow side region Outflow side region Partition Catalyst LengthLength Cell wall loading range from range from density thicknessPorosity amount Average pore inflow end Average pore outflow end(cells/cm²) (mm) (%) (g/L) diameter (μm) face (%) diameter (μm) face (%)Comparative 46.5 0.216 63 40 19 — 19 — Example 1 Comparative 43.0 0.21660 30 14 55 24 45 Example 2 Comparative 46.5 0.250 55 20 24 50 20 50Example 3 Comparative 38.8 0.216 60 30 13 20 20 50 Example 4 Example 146.5 0.216 63 40 13 40 20 40 Example 2 38.8 0.216 60 30 13 30 20 50Example 3 30.0 0.220 62 45 12 55 18 30 Example 4 40.0 0.310 61 40  9 5515 45 Example 5 42.0 0.250 63 35 11 40 19 50 Example 6 47.0 0.250 61 2014 60 19 35 Example 7 45.0 0.220 60 30 13 45 20 50 Example 8 47.0 0.25061 20 12 40 19 20 Example 9 38.0 0.300 62 30 14 60 16 40

For the honeycomb filter of Example 1, “Filtration efficiencyperformance” and “Exhaust gas purification performance” was evaluated inthe following manner. Table 2 shows the result.

(Filtration Efficiency Performance)

First, exhaust gas purification devices were fabricated by using thehoneycomb filters of each Example and Comparative example as the exhaustgas purifying filters. The fabricated exhaust gas purification deviceconnected to an outlet side of an engine exhaust manifold of a 1.2 Ldirect injection type gasoline engine vehicle, and the number of sootparticles contained in the gas emitted from the outlet port of theexhaust gas purification device was measured by a PN measurement method.“PN Measurement Method” is the measurement method proposed by theParticle Measurement Program (PMP) by the Working Party on Pollution andEnergy (GRPE) of the World Forum for Harmonization of VehicleRegulations (WP29) of the Economic Commission for Europe (ECE) of theUnited Nations (UN). More specifically, in the determination of thenumber of soot particles, the cumulative total number of soot particlesemitted after WLTC (Worldwide harmonized Light duty Test Cycle)mode-running was used as the number of soot particles in the exhaust gaspurification device to be determined, and filtration efficiency wasmeasured. With respect to the filtration efficiency measured asdescribed above, the value (%) of filtration efficiency of the exhaustgas purification device using the honeycomb filters of each Example andComparative example, when the value of filtration efficiency of theexhaust gas purification device using the honeycomb filter ofComparative example 1 was set to 100%, was obtained. The filtrationefficiencies were evaluated based on the following evaluation criteria.

Evaluation “Excellent”: When the value of filtration efficiency of theexhaust gas purification device using the honeycomb filter ofComparative example 1 was set to 100%, and the value of filtrationefficiency of the exhaust gas purification device using the honeycombfilter to be evaluated is 120% or more, the evaluation is regarded as“Excellent”.

Evaluation “Good”: When the value of filtration efficiency of theexhaust gas purification device using the honeycomb filter ofComparative example 1 was set to 100%, and the value of filtrationefficiency of the exhaust gas purification device using the honeycombfilter to be evaluated is 110% or more and less than 120%, theevaluation is regarded as “Good”.

Evaluation “Available”: When the value of filtration efficiency of theexhaust gas purification device using the honeycomb filter ofComparative example 1 was set to 100%, and the value of filtrationefficiency of the exhaust gas purification device using the honeycombfilter to be evaluated is 100% or more and less than 110%, theevaluation is regarded as “Available”.

Evaluation “Fail”: When the value of filtration efficiency of theexhaust gas purification device using the honeycomb filter ofComparative example 1 was set to 100%, and the value of filtrationefficiency of the exhaust gas purification device using the honeycombfilter to be evaluated is less than 100%, the evaluation is regarded as“Fail”.

(Exhaust Gas Purification Performance)

First, exhaust gas purification devices were fabricated by using thehoneycomb filters of each Example and Comparative example as the exhaustgas purifying filters. The fabricated exhaust gas purification deviceconnected to an outlet side of an engine exhaust manifold of a 1.2 Ldirect injection type gasoline engine vehicle, and the concentration ofNOx contained in the gas emitted from the outlet port of the exhaust gaspurification device was measured and purification ratio of NOx wasdetermined. With respect to the purification ratio of NOx measured asdescribed above, the value (%) of the purification ratio of NOx of theexhaust gas purification device using the honeycomb filters of eachExample and Comparative Example, when the value of the purificationratio of NOx of the exhaust gas purification device using the honeycombfilter of Comparative Example 1 was set to 100%, was obtained. Theexhaust gas purification performances were evaluated based on thefollowing evaluation criteria.

Evaluation “Excellent”: When the value of purification ratio of NOx ofthe exhaust gas purification device using the honeycomb filter ofComparative Example 1 is set to 100%, and the value of purificationratio of NOx of the exhaust gas purification device using the honeycombfilter to be evaluated is 120% or more, the evaluation is regarded as“Excellent”.

Evaluation “Good”: When the value of purification ratio of NOx of theexhaust gas purification device using the honeycomb filter ofComparative Example 1 is set to 100%, and the value of purificationratio of NOx of the exhaust gas purification device using the honeycombfilter to be evaluated is 110% or more and less than 120%, theevaluation is regarded as “Good”.

Evaluation “Acceptable”: When the value of purification ratio of NOx ofthe exhaust gas purification device using the honeycomb filter ofComparative Example 1 is set to 100%, and the value of purificationratio of NOx of the exhaust gas purification device using the honeycombfilter to be evaluated is 100% or more and less than 110%, theevaluation is regarded as “Acceptable”.

Evaluation “Fail”: When the value of purification ratio of NOx of theexhaust gas purification device using the honeycomb filter ofComparative Example 1 is set to 100%, and the value of purificationratio of NOx of the exhaust gas purification device using the honeycombfilter to be evaluated is less than 100%, the evaluation is regarded as“Fail”.

TABLE 2 Filtration Exhaust gas purification efficiency performanceperformance Comparative Criteria Criteria Example 1 Comparative FailGood Example 2 Comparative Acceptable Fail Example 3 Comparative GoodFail Example 4 Example 1 Good Good Example 2 Acceptable AcceptableExample 3 Good Excellent Example 4 Excellent Excellent Example 5 GoodGood Example 6 Good Acceptable Example 7 Acceptable Good Example 8 GoodAcceptable Example 9 Excellent Good

Examples 2 to 9

The honeycomb filters were manufactured in the same manner as in Example1, except that the cell density, the thickness and the porosity of thepartition wall, and the configuration of the inflow side region and theoutflow side region were changed as shown in Table 1. In theconfiguration of the inflow side region and the outflow side region inExamples 2 to 9, the average pore diameter of the partition wall (μm)and the length range from the respective end face (%) was adjusted bymaking the difference between the temperature in the filter of theinflow end face side and the temperature in the filter of the outflowend face side 10° C. or higher when firing the honeycomb formed body.Then, the platinum group element-containing catalyst was loaded to thehoneycomb filters of Example 2 to 9 in the same manner as in Example 1so as to have the loading amounts shown in the column of “Catalystloading amount (g/L)” in Table 1.

Comparative Examples 1 to 4

The honeycomb filters were manufactured in the same manner as in Example1, except that the cell density, the thickness and the porosity of thepartition wall, and the configuration of the inflow side region and theoutflow side region were changed as shown in Table 1. In theconfiguration of the inflow side region and the outflow side region inComparative Examples 2 to 4, the average pore diameter of the partitionwall (μm) and the length range from the respective end face (%) wasadjusted by adjusting the temperature distribution in the firingprocess. Further, in Comparative Example 1, the average pore diameter ofthe partition wall was set to 19 μm in any range in the extendingdirection of the cell of the honeycomb structure body by making thedifference between the temperature in the filter of the inflow end faceside and the temperature in the filter of the outflow end face side lessthan 10° C. when firing the honeycomb formed body. Then, the platinumgroup element-containing catalyst was loaded to the honeycomb filters ofComparative Examples 1 to 4 in the same manner as in Example 1 so as tohave the loading amounts shown in the column of “Catalyst loading amount(g/L)” in Table 1.

The honeycomb filters of Examples 2 to 9 and Comparative Examples 1 to 4were evaluated for “Filtration efficiency performance” and “Exhaust gaspurification performance” in the same manner as in Example 1. Table 2shows the result.

(Results)

The honeycomb filters of Examples 1 to 9 were confirmed to be superiorto each performance of the honeycomb filter of Comparative Example 1serving as a reference, in all evaluation of “Filtration efficiencyperformance” and “Exhaust gas purification performance”. Therefore, itwas found that the honeycomb filters of Examples 1 to 9 have excellenttrapping performance, also excellent purification performance. Inparticular, the honeycomb filters of Examples 1 to 9 were able torealize excellent exhaust gas purification performance even when theloading amount of the catalyst was relatively small (e.g., less than 50g/L). On the other hand, the honeycomb filter of Comparative Example 2was inferior to the honeycomb filter of Comparative Example 1 in thefiltration efficiency performance. It was considered that, in thehoneycomb filter of Comparative Example 2, the average pore diameter ofthe outflow side region was too large, and the partition wall of theoutflow side region did not sufficiently function as a filter medium fortrapping PM. On the other hand, the honeycomb filter of ComparativeExample 3 was inferior to the honeycomb filter of Comparative Example 1in exhaust gas purification performance. In the honeycomb filter ofComparative Example 3, the average pore diameter of the inflow sideregion was too large so that the catalyst penetrated into the poresformed on the partition wall and a catalyst layer contributing to theimprovement of exhaust gas purification performance was not formed.

INDUSTRIAL APPLICABILITY

The honeycomb filter of the present invention can be used as a filterfor trapping particulate matter in exhaust gas.

DESCRIPTION OF REFERENCE NUMERALS

1: partition wall, 2: cell, 2 a: inflow cell, 2 b: outflow cell, 3:circumferential wall, 4: honeycomb structure, 5: plugging portion, 11:inflow end face, 12: outflow end face, 15: inflow side region, 16:outflow side region, 17: intermediate region, 100: honeycomb filter.

What is claimed is:
 1. A honeycomb filter comprising: a honeycombstructure having a porous partition wall disposed so as to surround aplurality of cells serving as a fluid through channel extending from aninflow end face to an outflow end face; and a plugging portion providedso as to plug end at any one of the inflow end face side or the outflowend face side of the cell, wherein the cells having the plugging portionat ends on the outflow end face side and that are open on the inflow endface side are inflow cells, the cells having the plugging portion atends on the inflow end face side and that are open on the outflow endface side are outflow cells, the honeycomb structure has an inflow sideregion including a range of up to at least 30% with respect to the totallength of the honeycomb structure with the inflow end face of thehoneycomb structure as the starting point and an outflow side regionincluding a range of up to at least 20% with respect to the total lengthof the honeycomb structure with the outflow end face of the honeycombstructure as the starting point, in the extending direction of the cellof the honeycomb structure, an average pore diameter of the partitionwall in the inflow side region is 9 to 14 μm and an average porediameter of the partition wall in the outflow side region is 15 to 20μm.
 2. The honeycomb filter according to claim 1, wherein a porosity ofthe partition wall is 50 to 65% and a thickness of the partition wall is0.19 to 0.31 mm.
 3. The honeycomb filter according to claim 1, wherein acell density of the honeycomb structure is 30 to 50 cells/cm².
 4. Thehoneycomb filter according to claim 1, further comprises a catalyst forpurifying exhaust gas loaded on the partition wall constituting thehoneycomb structure, wherein the catalyst for purifying exhaust gas isloaded at least on the surface of the partition wall, in the inflow sideregion of the honeycomb structure.
 5. The honeycomb filter according toclaim 4, wherein the catalyst for purifying exhaust gas includes aplatinum group element-containing catalyst.
 6. The honeycomb filteraccording to claim 5, wherein the platinum group element-containingcatalyst includes an oxide of at least one element of aluminum,zirconium, and cerium.
 7. The honeycomb filter according to claim 4,wherein a loading amount of the catalyst for purifying exhaust gas perunit volume of the honeycomb structure is less than 50 g/L.